Steam-generating plant



J. E. BELL STEAM GENERATING PLANT Filed July 1, 1922 I5 Sheets-Sheet l INVENTOR M A TTORNEY Dec. 15 1925 1,565,305

J. E. BELL STEAM GENERATING PLANT FilegiJuly l, 1922 I 3 Shee'tS-She'et 2 x OooooooooooooooooocbtbO/oooooooooo OOOOO l OOOOOOOOOOOOOOOOOOOGOOOOOOOOOOOOOOOO 2" 0000000000 00 0000 00 0000 0000 0000 00 00 00 on 00 co as an 000000 000.00 no 0000 0000000000000000000000 0000 00 00 0000000000 000 00 a0 0000 00 00 000000 0000 0o c0 00 00 00 0o 00 00 no on 00 00 00 00 00 oo 00 0000 00 0o 00 00 00 0o 00 000 0 00 0000 000000 oo 00 no 00 0o 00 0000 .--fl 00000000 00 0o 00 00 oo co cc 0000 0o 00 e000 VIA/VENT R A TTORNLfY fi STATES JOHN E. BELL, OF BROOK LYN, NEW YORK, ASSIGNOR TO POWER SPECIALTY COM- means PANY, 03 NEW YORK, N. Y., A CORPORATION OF hl'EirV YORK.

STEAM -GENEBATING PLANT.

Application flied July 1,

To all whom it may concern: 3

i Be it known that I, J orrn E. BELL, a c1t1-' zen of the United States of America, residing at Brooklyn, county ofKings, and State of New York, have invented certain new and useful Improvements in Steam-Generating Plants, of which the following is a full, clear, and exact description.

The general object of my invention is to provide improvements in method of, and apparatus for generating steam. More specifically the object of my invention is to provide for the more effective utilization,

of an economizer for transferring heat to boiler feed water from the partially cooled products of combustion leaving the boiler furnace.

- It has long been common practice to preheatboiler feed water by the use of an economizer, but heretofore the economizer has ordinarily been regarded as an adjunct of the boiler, which, while of value, is distinctly of secondary importance as compared with the boiler proper. I have discovered,

however, that highly beneficial results, both with respect to the thermal efficiency and operating economy of a steam generating plant, and with respect to the initial construction and maintenance costs, may be obtained by making the economizer a more important element of the steam generating plant than has heretofore been the case.

To this end I substantially increasethe ratio of economizer heating surface to boiler heating surface over that heretofore employed in commercial practice, and provide the economizer heating surface in an economizer of special construction characterized by itscompactness and requiring a draft much stronger than is required'in the types of cconomizersheretofore in use to move the heating gases through it.- In the preferred practical mode of-carrying out my I o I 0 I inventlon I employ cconomlzer tubes Slll'lllar in construction to those heretofore employed in the well known Foster superheater, in that each tube comprises an inner tube of wrought steel which is surrounded an externally corrugated tubular cast iron casing; In the economizer which I "employ, the special tubes are preferably spaced closely enough together to give an aggregate external tube surface area perunit of volume of space occupied which is several times greater than is obtalned or is H22. Serial No. 572,166.

The special economizer tube construction employed provides a very large amount'of external heating surface swept by the heating gases, in comparison with the internal wet surface of the tube; is well adapted for high pressure work since the steel inner tube may readily be of suficient strength to resist an internal pressure as" high or higher than the boiler steam pressure, and the cast iron casing section protects the steel inner tube from the corrosive efiect of the furnace gases which rapidly destroy steel economizer tubes directly exposed to 4 the action of the heating gases, especially in the low temperature portion of an economizer.

Heretofore in ordinary practice, the ratio of economizer heating surface to boiler heat ratio of 7 to 10. In accordance with my present invention I" make the economizer heating surface at least as great as and in some cases considerably greater than the boiler heating surface. In thus increasing the ratio of economizer to boiler heating surface in a steam generating plant of given capacity, -I make the amount ofeconomizer heating surface greater and the amount of boiler heating surface smaller than has heretofore been used in a steam generating plant of similar capacity and efficiency. The increase in economizer heating surface made is less however than the decrease in boiler heating surface as my invention permit's of a smaller aggregate boiler and economizer heating surface than has heretofofe been required. The explanation of this saving in total heating surface is found in the fact that the decrease in boiler and increase in economizer heating surface tends to increase the average temperature differential between the boiler heating surface and the heating gases passing through the boiler, and also between the economlzer heating surface and the heating the absorption of the heat gases passing through the economlzer. The maximuni theoretical reduction in total heating surface would be obtained by increasing the ratio of economizer to boiler heating surface to the point at which the water would be heated in the economizer to the boiler steam temperature, but in practice I consider it desirable to maintain the maximum economizer water temperature below the boiler steam temperature under normal conditions of operation.

The rate at which a heated gas gives up its heat to a cooler surface is, as well-known, almost directly proportional to the velocity of flow of the gas over the surface, or more strictly speaking, to the product of the velocity times the gas density, or the mass flow. It is also a function of the temperature of the gas and increases very materially for gas temperatures corresponding to furnace temperatures. only due to the greater perature between the gas and the surface, which is, of course, but is also due to an increase in the transfer rate per degree difference in temperature. Heat absorbed by radiation from the furnace is roughly proportional to the fourth power of the absolute temperature of the furnace. ment of the furnace gases and before a uniform temperature gradient has been established, l have found that the heattransmitted by convection, or contact between the gases and the cooling surface is at a rate of difference in temabsorblng transfer of approximately the same order as that due to radiant heat. It follows therefore, that in a boiler, still or other apparatus, which absorbs heatfromfurnace gases, that the bulk of the heat so absorbed, which corresponds to high gas temperatures, is absorbed in such a manner as to make the velocity of the gases over the surface relatively unimportant. The same condition does not, however, exist in connection with given out at the lower gas temperatures, where the velocity is the controlling factor. I, therefore, propose arranging my boiler ;surface, which as has been pointed out,"is relatively of very much smaller extent thanhas heretofore been used, without regard to gas velocity, and ar-. range the economizer surface,which is much larger than heretofore used, to obtain the maximum allowable velocity compatible with the draft conditions. This necessitates a comparatively small draft loss in the. boiler portion, and a corresponding larger draft loss in the economizer portion to obtain the maximum temperature reduction with a given draft suction at the economizer outlet. The tubes should be horizontally disposed to restrict the tendency of furnace dust to deposit on the sides of the corruga- This increase is not of adhigh order,

In the case of first impingerof the furnace gases capacity than nseaeoa tion ribs and to facilitate cleaning the tubes. Furthermore, the tubes should extend transversely to the direction'of flow of the heating gases and should be arranged in rows substantially transverse to the direction of to flow of the heating gases, with the tubes in a adjacent rows staggered; and the tubes should be closely spaced so that the average distance between tube centers is small, for example in the neighborhood of one and one quarter times the maximum tube diameter, and the area of the gas path between a pair of adjacent tubes in adjacent rows trans.- verse to the direction of the gas flow should I not be less than one half the area of the gas path between adjacent tubes in the same row, to insure proper contact between the heating gases and the tubes, and to minimize the frictional resistance to the flow of the heating gases through the economizer and thereby minimize the draft required to move the heating gases through the bank of the economizer tubesQ I Where, as will ordinarily be the case, the high draft suction required for operating a steam generating plant in accordance with the present invention cannot be provided by stack or natural draft but requires an exhaust fan, I have found it advantageous to, make provisions for sending a portion only leaving the boiler proper through the economizer when the steam generating plant is operatiang under peak load conditions The diversion of a portion of the furnace gases away from the 1 economizer under peak load conditions permits of the use of an exhaust fan of smaller would otherwise be required, with a consequent decrease in initial and operating costs, and great economy in opera- 1 tion under normal loads. Moreover, the diversion of a portion of the furnace gases away from the economizer, under peak load conditions, 'does not result in a corresponding decrease in the temperature to which the feed water is heated. I

Where, as is frequently the case, the general direction of fiow of the heating gasesl is upward through an economizer or economizer section, which comprises a bank of horizontally disposed tubes, the tempera-. ture of the water in the tubes should in- I crease progressively from -the initial water temperature at the top of the bank to a maximum delivery temperature at the bottom of the bank. To obtain this result it is not only necessary to have the water flow back and forth through economizer tubes at successively lower levels, but it is also necessary, as I have discovered, to have a velocity of water flow through the 'economizer tubes which is not less thana certain critical velocity. If the velocity of the water I flow is less than this critical velocity parasitic'al or convection currents will be set up 3 Ill] in the water in the economizer tubes which will make the temperature in the-tubes at J. the top of the bank practically as high asf the temperature in the tubes at the bottom of the bank.

Where, in an economizer, the waterfiows serially through a plurality of tubes, and the conditions of operation are such as to maintain a fairly definite water temperature gradient along the path of flow, as is the case in an economizer comprising a bank of horizontally disposed tubes in which the water flows serially through tubes at successively higher levels, or flows serially at the proper velocity, as above explained, through tubes at successively lower levels, there is obtained the advantage that the corrosive efi'ects which occur mainly at a particular water temperature are substantially restricted to the tubes normally at that temperature, and are not distributed over all or a considerable portion of the tubes in the bank. This is particularly important in connection with the corrosive action on the inner surfaces of the tubes due to air contained in the water. As is well known, water which is exposed to the atmosphere at ordinary atmospheric temperatures holds in solution a considerable amount of air and when such water is heated, the air is liberated. In the case of an economizer the oxygen in the liberated air attacks or corrodes the inner surface of the economizer tubes when the latter are made of a ferrous material such as wrought iroir or steel. the liberated air thus attacks the economizer tubes is believed to be 180? or thereabouts. By arranging and-operating an economizer so that this critical water temperature of 180 or so, is normally maintaired in the economizer tubes in one ortwo rows only, and making the tubes subject to this corrosive action --readily.removable, it follows thatthe destructive efi'ect of'air in --the water is restricted to-a comparatively few number of tubes which may be readily replaced without disturbing the large ma jority of uninjured tubes. Q 1.

My invention comprises methods o f-and apparatus for elfectivelyutilizing the above mentioned discoveries and principles of op-. eration. The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however, its'advantages and specific objects obtained with it, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described preferred embodiments of my invention.

Of the drawings? Fig. 1 v is'a side elevation partly in section The water temperature at which,

is the economizer D which, in the construcarrangement of Fig. 3;-

Fig. 5 is a section on the line 5-5 of Fig. 3; I

Fig. 6 is a partial section on the line 66 of Fig. 1; and v Fig. 7 is an elevation partly broken away and in section of a modified form of economizer arrangement.

In the drawings, and referring first to the construction shown in Figs. 1 to 6, A" represents a boiler furnace of conventional type, with a water tube boiler B, above the furnace combustion chamberA. The boiler B as conventionally illustrated, comprises front and rear headers B and B? connected by inclined water tubes B and a steam and water drum B to which the rear headers are connected by conduits B and to which the front headers B are connected by horizontal tubes B. the furnace gases to travel across the water tubes in a plurality of passes from the 00111- bustion chamber A to the" furnace gas outlet A C are superheater tubes located in the space between the tubes B and B and between the first and second passes for the furnace gases.

Mounted above the boiler furnace proper ing preventing leakage through the joints in the shells D and D The tubes D each comprise an inner tube d of wrought steel Battles B and B cause heat insulating material, and also as apackl and an externally corrugatedtubular casing df formed-of cast iron sections which fit snugly on, and may be shrunk in place on the tubes 03. Various provisions may. be

made for supporting and connecting the different tubes D. In the simple and effective construction illustrated, the tubes D are supported in the end walls of the shell D and in an apertured tube sheet D placed midway between the end walls. One of the end walls is formed with apertures D a trifle larger-than the maximum diameter of the tubes D so that the latter may be axially removed from, and replaced in the housing through these apertures when con- L ditions' make this desirable.

The tube sheet D is formed with tube receiving apertures D similar to the apertures D The apertures D formed in the opposite end wall of the economizer housing are only large enough to receive the bare ends of the inner tube portion (1 of the tubes D. The tubular casings d of the tubes D abut against the inner side of the end wall of the portion of the shell D in which the holes D are formed, and at the opposite end of the economizer, the ends of the casings cl may well be substantially flush with the outer surface of the portion of the shell D in which the holes D are formed.

In the construction illustrated the tubes D in the top row of each economizer bank,

each has one end expanded or otherwise se.

cured in a supply header D Similarly the bottom row tubes D each have one end expanded or otherwise connected to the outlet header D of the economizer. In the particular construction shown, each of the economizer tubes in each intermediate row of the economizer is connected at one end by a return bend D to the corresponding end of the tube D in the row immediately above, and has its opposite end connected bya return bend D to an economizer tube in the subjacent row. As shown in Fig. 1 the economizer tubes in adjacent rows are staggered, and the side walls of the shell D are advantageously corrugated as shown in Fig. 1 in conformity to the staggered arrangement of the tubes D so as to restrict the flow of" the heating gases through the spaces between the side walls and the adjacent tubes D.

The two banks of economizer tubes are separated by a passage D which advantageously is formed with metal side walls D corrugated to conform to the staggered arrangement of the tubes D. The passage D forms a by-pass through which a portion of the heating gases may be passed under peak load conditions. Flow through the by-pass passage D may be controlled by a damper or dampers of any usual or suitable form. Preferably, however,,the special damper arrangement comprises a plurality of horizontally extending dampers E arranged one above the other in the passage 1). Each of these dampers may be rotated from a vertical Wide open position, into a horizontal closed position. In some cases each damper E may extend the full horizontal depth of the channel D, but in the construction shown, this channel is subdivided into four fiues by the tube sheet D and intermediate division walls I), and

- four dampers E, one for each flue, are provided at each damper level in the economizer. Each damper E may advantageously be formed, as shown best in Figs. 3, a and 5, of spaced apart sheet metal plates E connected together, and each damper is provided at its ends with a suitable pintle or spindle extension E which is journalled in the corresponding division or end wall of the channel D. As shown, the two aligned dampers at each side of the central division wall D are connected by a common pintle or spindle part E and each damper adjacent the end wall of the channel D has its corresponding pintle E projecting through the end wall and provided with an external cperating connection. The operating connections forv the dampers E shown, comprise a gear segment E connected to the outer end of each externally projecting pintlc E, and an operating shaft E at each end of the economizer provided with worm sections E in mesh with the corresponding gear segments E As shown each shaft is provided with a hand wheel E by which it may be rotated to open and close the corresponding dampers. In its closed position each damper section extends into close proximity to the adjacent portions of the by-pass side walls D (see Fig. 5) but need. not make a perfectly tight joint with the latter since, in accordance with the principle involved in the ordinary labyrinth packing, the series of dampers E in each fiueportion of the bypass serve, when closed, to prevent any appreciable flow through that flue portion, even though the joints at the edges of any one damper E in the series are open enough to permit an appreciable flow through those joints if subjected to the pressure difierential at the opposite ends of the flue.

The fact that in the by-pass damper ar- Lsincewith this construction, contraction and expansion or distortion of the parts resulting from the varying temperatures to which they are subjected do not interfere with the operation or eifcctivencss of the dampers. To permit the removal and replacement of the dampers the central division wall D, the intermediate division walls I) and the portions of the shell D at the ends of the bypass channel D are formed with slots D large enough to permit the passage therethrough of the dampers when the latter are vertically disposed and are 1a1sed upward from their normal positions in which the pintles E rest against the bottom edges of these slots. Removable covers D may be provided for the slots 1) in the shells D and D but the slots D in the division wall D and intermediate walls D need not be closed.

The connection F between the economizer housing proper and the boiler housing for passing the furnace gasesto the economizer from the boiler housing outlet A is advantageously formed, similarly to the economizer housing, with inner and outer metallic shells and insulating material between the shells. 1 Above the economizer is located an exhaust fan G for creating the draft suction required to move the furnace gases through the boiler and economizer at the desired velocity.v The connection H betweent the exhaust fan casing proper, and the economizer housing is advantageously formed or metal which need not be insulated as' heatradiation from the shell is desirable since it reduces e temperature and volume of the gases pa ing from the .economizer and the heat thu stlost would not be utilized in the apparatus in any event.

The feed water is supplied to the economizer by a supply pipe I ordinarily connectcd to the outlet' of a boiler feed pump (not shown). 'The pipe I is connected to the top economizer header 1)", and the boiler feed water is forced through the economizer tubes and int; the boiler against the pressure of the latter through the conduit J connectmg the bottom economizer header D to the steam and water drum B In many cases I prefer to employ a boiler 0 feed controller automatically regulating the flow of feed water into the boiler 1n response to the requirements, and this may operate in a known manner either to directly control the delivery of water to the economizer, or to directly control the flow of water from the economizer into the boiler. In any event the pressure of the water in the economizer tubes must be as high as, and in some cases may be appreciably above the pressure in the steam and water drum B of the boiler, which will ordinarily be 250 pounds or above, in steam generating plants constructed in accordance with the present to which it is subjected, while the cast iron casing d is to a large extent immune to-attack by the furnace gases, and such pitting or other in ury as it may receive in time from the corrosive effect of the furnace gases does not weaken the resistance of the tubes to theinternal bursting pressure towhich they are subjected, and does not appreciably efiect the heat absorbing capacity of the cast iron casing. This heat absorbing capacity is of .course greatly enhancedby the relatively great amount of external heating sur-- face 1n contact with the furnace gases which it provides. The area of external gas swept heating surface of each tubeniay advanta-' geously be in the neighborhood of 5 to 6 times as great as in the internal wet surface area of the tube.

In the construction shown in. Figs. 1 and arranged in rows extending parallel to the general direction of gas flow, the tubes in the adjacent horizontal or transverse rows being staggered. The tubes D are closely spaced. In ordinary practice I prefer to makethe average of the distances between the centers of each tube 1) and the centers of the immediately adjacent tubes about one and one quarter times the maximum tube diameter. Notwithstanding the small space betweenthe exterior surfaces of the economizer tubes, the internal tubular parts d are sufficiently, far apart to permit the 1 ready use of suitable end connections between the difl'erent tubes, since these con nections are external to the inner metal shell D of the economizer housing, and the tube casings d need not project through the shell D With this spacing the external heat absorbing surface if the economizer per unit of space occupied by the bank of economizer-tubes is several times greater than is practically possible with economizer tubes of the same lnternal diameter and having smooth external walls, especially since with the smooth walled tubes the m nimum distance betweenthe tubes is limited by the necessity for providing space for the necessary end connections to the tubes. 1

Suitable provisions should be made for blowing or washing dust oil of the economizer tubes at sufllciently frequent intervals. In the referred construction illustrated, the provisions for this purpose comprise water spray pipes K horizontally disposed above the banks of economizer tubes and extending transversely to the tubes, and suitable connections for supplying water at intervals to these spray pipes. Advantageously the water supply connections are arranged so.

that water is discharged from only a few-of the pipes K at a time, to thereby avoid undue cooling of any one economizer tube as awhole, and to avoid the disturbance in draft conditions which would be createdby the .very considerable volume of steam which taneously discharged from all of the spray pipes Suitable pocketed) may advantageously be provided, as shown, atthe bottom of the economizer housing to recelve the liawould be generated if water were simul- Y clean-olf water and-dust with valved drain pipe connections D "'discharging from the' pockets.

In the contemplated construction and: mode of use of the apparatus shown in F1 1 to 6, the aggregate heating surface of t e economizer swept'by the heatin gases is at,

least as great as the aggregate eating surface of the boiler proper so that a. much larger portion of the total amount of heat less of the boiler heating surface. The diseconomizer heating makes it possible to amount of superheat tribution of boiler and surface whieh I employ obtain a relatively high 7 with a superheater of moderate size located above the main bank of water tubes.

The close spacing of the economizer tubes, and their corrugated exterior surfaces provide tortuous gas paths through which the heating gases move with relatively high velocity thus insuring, a high heat transmission factor and a large economizer capacity per unit of volume. The consequent comparatively small economizer volume required for a given duty makes it practically feasible to employ an economizer housing which is substantially air tight, thus practically elimi nating air leakage into the economizer not withstanding the comparatively high draft suction required to move the heating gases through the boiler and economizer. Air leakage is objectionable both because of the cooling efiect of the air leaking in, and also because of the resultant increase in volume of the gases which must be handled by the draft creating fan. Air leakage tending to increase the exhaust fan capacity required is especially objectionable in the practice of my invention because the relative'high draft suction which I ordinarily employ requires a considerable expenditure of fan driving energy at normal load even when there is no leakage at all. lit has heretofore been the practice to operate a boiler plant comprising an economizer with a draft suction which ordinarily does not exceed one and three quarter inches of water, at a maximum.

lln proceeding in accordance with the present invention it may advantageously employ.

a draftsuction at normal load as big three, four, or five inches of water, and of which much more than hall is utilized in moving the heating gases through the economizer.

The relatively high draft suction at normal load which I prefer to employ, makes the economizer by-pass D of especial importance, as becomes apparent when account is taken of the great increase in exhaust fan capacity and driving power which would he re quired if all the heating gases were drawn through the economizer under the peak load conditions which may prevail for an hour or so out of each twenty-four hours of service; Assume, for example, a plant in which the boiler heating surface proper is square feet, and the normal load involves operatlon of 400% of rating, while for an hour or so out of each twenty-four hourt, the boiler must be operated at 640% of ratmg; and also assume that when operating product of the volume of ten thousand.

tion must be increased from vt hree'inches to times three inches or about seven and twothirds inches. lhe fan driving force required for operating the fan at the increased load will be increased, in proportion to the gas handled and the suction required to move the gas; in other words, the driving force required for the fan under peak load conditions will be, not 20 H. 1 but 8 '8 2 5 5 times 20 H. P, or about 82 H. P. Actually the temperature of the gas at the fan inlet will be higher under peak load conditions the volume of gas drawn of the volume of gas at normal load; the

draft suction necessary to move this gas through the economizer will be about one and one-eight (i. e.

gas through the economizer will be a little over 24: H. P. (i. e.

with the by-pass D open will heat the draft suction at the fan are then drawn through the boiler feed water in the economizer up to, or

nearly to the temperature to which it is heated in normal operation.

The effective utilization of my compact economizer requires a progressive -graduation in temperature of the water flowing through the eeonomizer from the water inlet temperatttre at the top of theeconomizer, to thedelivery temperature at the bottom of the economize-r. I have found that this result can be obtained in an economizer in which the general direction of flOW'Of water through a bank of horizontally disposed "tubes is downward, only when the velocity of Water flow through the economizer tubes is equal. to,or above. a certain critical velocity.

If the velocity of water flow through the economizer tubes is less than this critical velocity, there is a tendency to the maintenanceof parasitical or convection currents in the water in the tubes substantially equalizing the Water temperature throughout the economizer tube system, so that the temperature in the upper economizer tubes will be practically ashigh'as the temperature in the lower tubes of the economizer. The exact critical velocity which Inust be equaled or exceeded to insure the, de-

sired temperature graduation from top to bottom of an economizer in which the water flow is downward depends upon a number of factors, some of which are difiicult to predetermine with precision.

The critical velocity may be readily de-.

' utilization of this feature of my invention 1 connect the tubes of the economizer so that the normal rate of flow through the econo mizer tubes at the lowest rate of evaporapaths of flow between the economizer inlet and economizer outlet. If the tubes in each horizontal row were connected in pairs so that the water entering, one end of a tube would pass through that tube to the oppo site end of the economizer, and would then return through another tube in the same row before passing to a tube in a lower row, there would be but seven paths of water flow through the economizer, and the velocity of fiow fora given quantity of water flowing would be twice as great as in the. instance first given. As already explained, the efi'ect of maintaining a definite graduation of water temperature in the economizer tubes is to confine the internal corrosive action of liberated air to the comparatively .few tubes in which the normal temperature is that at which the corrosive action mainly occurs. Thus, if in the economizer shown in Fig. 1, the temperature in the tubes at the level indicated by the line X, is normally about 180", the corrosive action of liberated air will be mainly confined to the tubes at that level. With the described method of mounting and. connecting the tubes, it will be, apparent to those skilled in the art that any particular tube or tubes may be readily replaced. With the particular form of end connections illustrated, the replacement of the tube elements involves cutting off the ends of the inner tubes (Z of the cor responding elements which are readily accessible for this purpose, after which the elements are axially'removed through-the openings D and D in the tube supporting Walls D and D respectively. It Will be understood, of course, that the metallic outer wall D is formed with removable sections to permit tube replacements, but the particular provisions made for this purpose form no part of my present invention and hence are not illustrated herein.

In Fig. 7, I have shown a modified form of economizer in which the economizer tubes D are arranged in two banks D and D sepa} rated by a partition D and arranged in an economizer housing provided with an inlet D for heating gases opening to the under side of the tube bank D and with a chamber D through which the heating gases pass tion at which it is contemplated to operate from the top of the bank D into the top the boiler for any considerable portion of the time will be at least'as high as the critical velocity. It is apparent, of course, that the velocity offlow through the economizer tubes depends on the number of separate paths of flow provided between the economizer inletand outlet. Thus in the economizer in which there are fourteen economizer tubes each horizontal row, if the economlzer tubes areconnected (as shown in Figs. 1 and '2) so that each tube in one row is separzitely connected to a tube in the adjacent row there will be fourteen of the bank D and with an outlet D for the spent heating gases opening from beneath the tube'bank D The external walls of the housing of the economizer DA may be similar in construction to the housing walls of the economizer D- In the economizer -DA the water to be heated passes initially through the header D into the tubes D in the lower row of the tube bank D Thence the water passes upward throu h the tubes in the bank D to a top header D to which the various tubes .in the top rows of both tube banks D and D are connected. From Cal the header D the water passes downward through the tubes in the bank D to the header D to which the tubes in the lower row of the bank D are connected. From the header D the water may pass to the boiler through suitable connections not shown.

In each of the tube banks 1) and D of the economizer DA the general direction of water flow is counter to the flow of the heating gases through the intertube space of the tube bank. To obtain the full advantage of this counter flow, the velocity of water flow through the tubes in the bank I) must be equal to or exceed the critical velocit previously mentioned. In so far as the bank I) is concerned, however, the desired water temperature graduation from bottom to top of the bank will be obtained regardless of the velocity of flow through the individual tubes of the tube bank, and the tubes D of the bank D may be so connected as to give a flow velocity through them which is less than the critical velocity if condition this desirable.

In the economizer DA, ports D are formed in the portion of the wall D beneath the two banks D and D Dampers EA are provided to regulate the flowof heating gases through the ports D which thus provide a by-pass about both banks of economizer tubes between the inlet D and outlet D through which a portion of the heating gases may be passed under peak load conditions. To avoid all possibility of undesirable steam and air accumulations in the top economizer headers, and to guard against excess pressure in the economizers, the top header D of the economizer D, and the top header D of the economizer DA may each be provided with one or more pressure relief or safety valves L Certain novel features of construction and arrangement disclosed but not claimed heremakes in are claimed in my co-pending application, Serial No. 336,284, filed November 7, 1919, of which this application is, in part, a continuation.

While in accordance with the provisions of the statutes, l have illustrated and described the best forms of carrying out my invention now known to me, it will be ap; parent to those skilled in the art that changes in the form of the apparatus and modes of operation described herein may be made without departing from the spirit of my in= Yention as set forth in the appended claims, and that certain features of my invention may sometimes be used to advantage without a corresponding use of other features.

Having now described my invention, what ll claim as new and desire to secure by Letters Patent. is:

1. In a steam generating plant comprising a boiler furnace and a boiler section havlng' water, and having a steam and water space,

the improvement which consists in an economizer section traversed by the boiler furi nace heating gases after the latter have left the boiler section and through which water is passed into the boiler section, and formed of staggered rows of steel tubes encased in externally corrugated tubular cast iron sections, said tubes being so proportioned as to provide an aggregate economizer heating surface approximately as great as the aggre gate boiler heating surface, to require a move the heating gases omizer section at least as suction required to move through the boiler section;

2. The combination with furnace, of an economizer comprising a ban of horizontally disposed tubes externally swept by the heating gases leaving the furnace and through which feed. water=is passed into the boiler, said tubes being each provided, with external circumferentially extendingribs proportioned and disposed to make the external surface area of the tube several times greater than its internal surface area, and being each of a length many times greater than its maximum diameter,

through the econa boiler and its and so spaced as draft suction at normal load to v great as the draft the heating gases 1 and being spaced to provide an external tube surface area per unit of space occupied by said bank which is several times greater than is practically possible with tubes which are of the same internal diameter and have smooth outer walls.

3, The combination of claim 2 further characterized by the fact that each of the economizer tubes com rises an inner thin walled steel tube, an therefor of tubular form and externally cerinsulating material in which-the portions of said tubes projecting through said walls and said return connections are embedded, and which engages the outer sides of said walls and minimizes gas leakage through the latter.

5. The method of operating an economizer comprising a bank of horizontally disposed tubes connected to provide paths of water flow between the tubes at the top of the bank and the tubes at the bottom of the bank a cast iron casing body portions and havpassing successively tlirough intermediate tubes at different levels, which consists in passing heating gases upward through the inter-tube space of the bank, and passing the water along said paths of flow from the top to the bottom of the bank with a velocity of water flow through the tubes in excess ofthat permitting equalization of temperature in tubes at different levels by convection currents of the water in the tubes.

6. The combination with a boiler furnace, of means providing an outlet passage for the heating gases issuing from said furnace, a bank of economizer tubes traversing a portion of said passage and a conduit having imperforate walls connected at its ends to said gas passage to form a by-pass about the portion of the latter traversed by the economizer'tubes, and a series of dampers distributed along the length of said conduit and each adjustable from an open position into a closed position in which it substantiallycloses but does not entirely seal the conduit.

1 7. An economizer comprisinga casing provided with an inlet and an outlet for heatmg gases, and to banks of economizer tubes located therein and providing parallel paths of flow for the heating gases between the 1 inlet and outlet and spaced apart from one another to provide between them a by-pass between said inlet and outlet, and means the heating gases with the tubes ineach such row staggered with respect to the tubes in each adjacent row, and vwith the tubes, in the difierent rows so spaced that the area of the gas path between any two adjacent tubes in' adjacent rows is not less than half of the area of the gas path between two adjacent tubes in the same transverse row.

In testimony whereof '1 hereto afix my signature.

JOHN E. BELL. 

